Parallax correction circuit



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Sept. 23, 1952 3 Sheets-Sheet 1 Filed June 23, 1944 COARSE Dl FFERENTiALAzmufn GUN TURRET REC.

ELEVATION DIFFERENTIAL :II I .2 RN mm mm m 7 u A W A m P 23, 1952 G. E.WHITE EI'AL PARALLAX CORRECTION cmcun 3 Sheets-Sheet 2 Filed June 25,1944 INVENTORS'. GIFFORD E. WHITE L. GRAEF- L'AFOEZZP ROBERT PatentedSept. 23, 1952 UNITED STATES PATENT OFFICE PARALLAX CORRECTION CIRCUITGifiord E. White, Hempstead, Robert L. Graef, Brooklyn, and Charles J.La Forge, Hempstead, N. Y'., assignors to The Sperry Corporation, a

corporation of Delaware Application June 23, 1944, Serial No. 541,750

1 a relatively low cost, a compact light weight parallax correctingapparatus suitable for use on airplanes having guns controlled fromcomputing mechanism at a central sighting station.

The desirability of parallax correction is recognized and variousdevices have been proposed for the purpose of computing parallaxcorrection angles. A parallax correcting system is disclosed in theItalian patent to Zeiss No. 362,981, issued September 14, 1938, and inthe abandoned Papello application Serial No. 212,349, filed June 7,1933, and published May 25, 1943, by the Alien Property Custodian. Aparallax correcting apparatus for inter-aircraft fire control isdisclosed in the patent application of Knowles and Harris, filed March1, 1943, Serial No. 477.666, now Patent No. 2,428,372, issued October21, 1947.

In view of the known prior art of fire control and parallax correction,it is not thought necessary to give here a detailed discussion of theproblems involved in determining parallax correction angles, as thissubject is known to those skilled in the art.

In one embodiment, the invention contemplates a central station whichmay be provided with separate port and starboard computing mechanisms,each being controlled by any suitable target tracking device. Switchingmeans are provided by which the respective computing mechanisms may becoupled, if the need therefor arises, to the guns on the opposite sideof the craft.

In the embodiment of the invention about to be described, gun aimingdata from a computer is transmitted to the gun turrets by suitable meansfor reproducing angular motion at a distance, a preferred datatransmission device being a known type of self-synchronous motor.Differential transformer devices connected in the circuitsinterconnecting transmitter and receiver self-synchronous motors havetheir rotary members offset under control of the parallax correctingcircuits to effect the required parallax correction of the gun turrets.

The invention will now be described with the aid of the accompanyingdrawings of which? Figs. 1 and 2, when placed side by side, show awiring diagram of an embodiment of the invention;

' Fig. 3 is a block diagram showing another form of the invention; and

Figs. 4 and 5 show details of transformer windings.

The production of the present apparatus is simplified by the use ofstandard radio tubes. These tubes have well known characteristics whichare fully described in various tube manuals.

In computing fire control data for controlling the directing of a gunmounted on an airplane toward a target, five variables are usually usedfor accurate determination of the ballistic and prediction corrections.These variables are azimuth, elevation and slant range, air speed andaltitude. In addition, the rate of change of the target azimuth,elevation, and range are needed to permit computation of the futureposition of the target. Gun aiming angles are derived by the computingmechanism from these variables and transmitted to the gun turrets toeffect a corresponding positioning of the guns. The parallax computer ofthe present invention modifies the data transmitted to the gun positionsfrom the control station to compensate for parallax due to the spacedrelationship of the cenl/li tral station and gun positions.

In a preferred embodiment of the invention, the computation ofcorrection angles involves the use of electronic circuits and computingtransformers. The computing transformers are high impedance transformerswhich receive their inputs from the data transmission lines of thecontrol station without any noticeable load on them. The outputs fromthe secondary circuits of these transformers are proportional to thesines and cosines of the control station transmitters in gun azimuth(Ag) or gun elevation (Eg).

Two types of electronic circuits are required. The first is a phasesensitive multiplier circuit which takes two alternating current signalsand gives out an alternating current signal whose amplitude isproportional to the product of the amplitudes of the input signals. Thesecond is a reciprocal circuit which takes two alternating currentsignals and gives out an alternating current signal which isproportional to the ratio of the amplitudes of the input signals.

Uncorrected data comes from the transmitters of the control station tocorresponding electrical differential transformers, each having athreephase rotor and a three-phase stator. The rotary members of thedifferentials are rotated under control of the parallax correctingcircuits according to the proper correction angles, and the correcteddata of their outputs are used to control the receiver motors whichposition the gun or turret. Another rotary transformer is geared to eachset of the electric differentials and measures their positionelectrically. The output of the rotary transformer is fed back to theservo amplifier input where it bucks the computed correction signal. Thedifference in signals is fed to the amplifier which in turn operates theservo motor which drives the electric differentials until thedifferentials have reached their proper positions where the signaldifference is zero.

The parallax correction arrangement herein described may be also appliedto an automatic gun laying system, or the like, using a radar scanner orany other system where parallax correction is desirable.

One embodiment of the invention contemplates parallax correction asapplied to the most practical arrangement of control station and gunturrets wherein the control station and turrets are substantially inalignment along the longitudinal axis of the airplane.

When the control station and turrets are so positioned along thelongitudinal axis of the airplane, the azimuth correction angle isclosely proportional to the sine of the gun azimuth angle (Ag) dividedby the product of the cosine of the gun elevation angle (E and slantrange (Do) and the elevation correction angle is closely proportional tothe cosine of the gun azimuth angle multiplied by the sine of gunelevation angle and divided by slant range. The circuits by which thesefunctions are computed electronically will now be described.

In the control station, shown in Fig. 1, coarse and fine azimuthtransmitters and 2| have the respective phase windings of theirthreephase rotors connected to corresponding phase windings of thethree-phase stators 22 and 23 of coarse and fine azimuth differentialtransformers 24 and 25 of the parallax correcting circuits. Thethree-phase rotors 26 and 21 of these differential transformers havetheir respective phase windings connected to corresponding phasewindings of the three-phase stators 28 and 29 of coarse and fine azimuthturret receivers 30 and 3|. The rotor windings of the turret receivers30 and 3| are energized from a source of alternating current as are thestators of the computer transmitters 20 and 2|.

In the same manner, the elevation transmitters 32 and 33 of the controlstation are interconnected with the stators of coarse and finedifferential transformers 34 and 35, whose rotors are similarlyconnected to the stators of elevation turret receivers 36 and 31. Therotors of elevation turret receivers 36 and 31 and also the stators ofthe corresponding elevation transmitters in the control station areenergized from a source of alternating current.

Differential transformers 25, 24, 34 and are so constructed that whenthere is no difference in mechanical position between rotor and statorthe transformer ratio thereof is 1:1. When there is no parallaxcorrection, the rotors and stators are thus aligned and the turretreceivers will be positioned as though they were connected directly tothe transmitters of the control station.

If the differential transformer rotors are rotated through some fixedangle, the new voltages induced in the rotor windings thereof will bethe same as the voltages would be in the control station transmitterstator windings if the rotors associated with the latter had beenrotated through the same angle. Thus, if the rotors of the differentialtransformers are rotated through an angle corresponding to the necessarycorrection 4 for parallax, the turrets will move away from the positionof the transmitter by the corresponding correction angle.

Motors 40 and 4| are controlled by the parallax correction amplifier,described further on. These motors are driven in one direction or theother, and through proper gearing, indicated by dot-dash lines, turn therotors of the differential transformers through the necessary correctionangle, thereby inserting the parallax correction.

The parallax correction circuit has its input connected to theself-synchronous motor circuits through four trig-function transformersof novel construction having output functions proportional to sines orcosines of the control station transmitters. The primary windings of thetransformers are energized from the wires interconnecting the coarsetransmitters of the control station and the differential transformers.

Each of the four trig-function transformers comprises three separatetransformer units, the respective primary windings of the transformerunits being delta connected and energized by the circuitsinterconnecting the coarse control station transmitters and the coarsedifferential transformers. The circuit details of the transformer unitsare shown in Figs. 4 and 5. The respective secondary windings of eachtransformer are connected in series, and the turn ratios are such thatthe magnitude of the output of alternating current is directlyproportional to the desired trigonometric functions of the actual A2 andEg angles and the phase of which (0 or degrees) reverses as thealgebraic signs of the functions change.

Referring to Fig. 4, with the described primary connections, where e1.oz, and e; are amplitudes of the A. C. voltage, and 0 the angle ofrotation of the Selsyn, then in the primary windings of the respectivetransformer units T1, T2 and T3 ei=E sin 0 e2=E sin (0+120) ea=E sin(0l20) and in the secondary windings,

and the total secondary voltage and T are functions of T1, T2, and T3and can be made any desired values. The particular values of =0 and =90give a sine and a cosine function respectively.

The transformer shown in Fig. 5 is the trigfunction transformer 45 forsin Eg. This transformer differs from the other trig-transformers inthat each transformer unit is provided with two secondary windings,corresponding windings of each unit being connected in series and oneterminal of each of the serially connected windings being joined to thecorresponding terminal of the other windings to provide a center tap fora circuit to take care of positive and negative values of sin Eg.

Transformer 45 has the three terminals of its delta connected primarywinding connected to elevation Selsyn leads 46, 41 and 48. Its secondaryis center-tapped as shown in Fig. 5, and across each section of theoutput are connected serially connected resistances 49 and 50.Resistance 49 has a resistance of approximately forty thousand ohms.while that of resistance 59 is ten thousand ohms. The center tap isconnected to the secondary winding of transformer whose primary isenergized from a source of alternating current. The output oftransformer 45 is an AC. voltage proportional to sine Eg.

A vacuum tube 52 (Fig. 2) known commerically as a 6H6 tube, which is adouble diode, has its cathodes 53 and 54 connected by circuits 55 and 56to the junction points between the respective resistors 49 and 59.

The plate 51 of the diode is connected through a half megohm resistor 59to the control grid of a vacuum tube 69 of the 68K? type. Plate 58 issimilarly connected to the control grid of another tube 6|, also of the68K? type. The cathodes of both tubes 69 and 6| are connected to ground.An output load network is provided for tube 52 composed of half megohmresistors 62 and 63 and condensers 64 bridged across plates 51 and 58and connected at its midpoint to ground. Conventional screen grid andsuppressor grid connections are employed for tubes 69 and 6 I. It willbe understood that suitable filament circuits are used with the varioustubes although none are shown.

The control grids of tubes 69 and 6| are also connected respectivelythrough condensers 65 and 66, and circuit 61 through resistances 68 and69, of forty thousand and twenty thousand ohms respectively, to oppositeterminals of secondary winding 19 of a trig-function transformer 1|having a turn ratio such that the magnitude of the secondary voltage isproportional to cos Ag, the primary being energized from the leads 12,13 and 14 which interconnect the azimuth coarse differential transformerwith the corresponding transmitter of the control station. With thearrangement just described, the grids of tubes 69 and 6| are energizedby voltages proportional to sin Eg and cos Ag, the output of the tubesbeing arranged to produce and A. C. current proportional to sin Ea X cosAg. The output circuit of tubes 69 and GI will be taken up again afterthe operation of the circuits of tubes 52, 69 and 6| has been described.

Assuming that Eg is zero degrees, then sin Eg, the voltage at the outputof transformer 45 is also zero. In this condition, the two cathodes ofdouble diode 52 are always at the same potential with respect to oneanother. The center tap of the voltage divider 49-49 in the cathodecircuit receives an A. C. voltage from transformer 5| with respect toground. When the cathodes swing negative in potential, the plates of thedouble diode which are connected to ground through resistances 62 and 63are at a higher potential than their cathodes and both sections of thediode will conduct. This will cause a voltage drop across the two loadresistors 62 and 63, and the condensers 64 associated therewith willcharge. Both plates will become negative with respect to ground. Thecondensers will discharge slightly during the next half cycle when thecathodes swing positive and there is no plate current. In other words,the tube will act as a retifier and the plate voltages will be D. C.voltages. The magnitude of the negative plate voltages depends on the I.R. drops in resistances 52 and 63, which in turn depend upon the platecurrents. The plate current in a diode depends upon the difference inpotential between the cathode and plate. Thus, the cathode volttagedetermines the D. C. plate voltage. Both plate voltages of the doublediode 52 are approximately 8 V. when sin Eg=0.

Assuming now that sin E3 is not zero, and that the output of transformer45 is such that during the negative swing of the cathode voltage, theupper terminal of the secondary winding is more negative than thelowermost terminal of the winding. With this condition cathode 53 willgo more negative and cathode 54 less negative as the transformer causesan alteration in cathode voltages. As stated above, the cathode voltagedetermines the D. C. plate voltage, and hence plate 51 will become morenegative and plate 58 less negative due to this particular sin E3. Thechange in the two plate voltages depends upon the change in cathodevoltage, and since this change is proportional to sin Eg, the platevoltage is proportional to sin Eg. If sin Eg increases, the change inplate voltage increases. If the guns are moved by the transmitters ofthe control station to the other side of zero degrees, the algebraicsign of sin Eg changes. In this case, the lower terminal of thesecondary winding of transformer 45 will be negative with respect to theupper terminal thereof during the negative swing of the cathode voltage,and now, plate 58 will become more negative, and plate 51 will becomeless negative. Thus, one plate voltage of the double diode becomes morenegative than -8 V. (from transformer 5|) by an amount proportional tosin Eg, while the other plate voltage becomes less negative by an equalamount, and Which plate is more negative and which plate is lessnegative depends upon whether sin Eg is positive or negative.

Tubes 69 and 6| are well known super control amplifier tubes of a typeused in many radio sets. The characteristic of this type tube is aremote cut-off with a variable amplification. factor. Curves showing thecharacteristics of this tube may be found in almost any radio tubemanual.

The amplification factor can be defined as the ratio of the incrementalchange in plate voltage to the incremental change in grid voltage whichcauses it; that is, the change in plate voltage is equal to the changein grid voltage multiplied by the amplification factor. In this type,the amplification factor varies with changes in the grid bias.

Since tube 52 supplies the grid bias for tubes 69 and GI, the effect ofsin Eg on these tubes is to change their bias, and since changing thegrid bias changes their amplification factors, the amplification factorof one becomes larger while that of the other becomes smaller, dependingupon whether sin E; is positive or negative.

The output of trig-function transformer II is a voltage proportional tocos Ag. This voltage is used as the A. C. signal voltage applied to thegrids of tubes 69 and 6|. Since the change in amplification factor isdirectly proportional to sin Eg, and since the grid signal is cos Ag,the plate voltage of tubes 69 and 6| will vary as the product (cos Ag)(sin Eg). The bias on one tube will increase, while the bias on theother tube will decrease. In one case, the amplification factor willincrease with an increase in sin Eg. and in the other case, theamplification factor will decrease with an increase of sin Es. Thus, theA. C. plate voltage will increase in one tube, for instance, tube 69,but will decrease in the other tube 6|. A difference in the A. C.component will appear on the plates and an A. C. current will flow inthe primary winding 89 of transformer 8|.

The terminals of primary winding 89 of transformer 8| are connectedthrough condenser 82 to the respective plates of tubes 60 and 6|. Twofifteen hundred ohm load resistances 83 and 84 are connected between theplates, and their junction point is connected to a source of D. C.potential. This is a conventional arrangement for eliminating thebiasing effect of a. D. C. plate voltage on the primary winding of atransformer.

The secondary winding 85 of transformer 8| has one terminal connected tothe control grid of a tube 81, which is of the 6SK7 type. The oppositeterminal is connected through condenser 86 to the cathode of the tubeand also through a resistance 88 and circuit 89 to a plate of tube 90which is a 61-16 double diode. The corresponding cathode of the latteris connected via circuit 92 to the arm 93 of the potentiometer 94 of arange solution device at the control station. The potentiometer isconnected through a dropping resistance 95 to a source of A. C.potential.

The cathode voltage of diode 90 is controlled by the operation of thepotentiometer, the plate of the diode becoming more negative as therange increases. This plate voltage is used to apply grid bias to tube81, and since the bias increases as the range (Do) increases, theamplification factor decreases as the range increases. The circuit is sobalanced that the amplification factor varies inversely as the range.Thus, the A. C. plate voltage component of tube 81 (which equals theproduct of the A. C. grid signal and the amplification factor) isdirectly proportional to the product: (cos Ag) (sin Eg) o).

This is the expression for elevation parallax correction and it includesall of the variables.

A rotary transformer 96 having windings such that its output is a linearA. C. voltage of a magnitude proportional to the angular displacement ofits rotor, has its stator energized from a source of A. C. current, andits rotor coupled by suitable gearing, indicated by dash-dot lines, tothe differential transformer rotors. The rotor winding of rotarytransformer 96 is connected via circuits 98 and 99 to opposite terminalsof a twenty thousand ohm potentiometer I00. An eight thousand ohmresistor ml is included in circuit 98. The arm I02 of the potentiometeris connected to one of the control grids I03 of a vacuum tube I05. Thepotentiometer can be adjusted to give a matching voltage, which takesinto account the distance between the sighting station and the gunstation. v

Tube I05 is a twin pentode amplifier of the 1644 type each section ofwhich consists of a plate, suppressor, screen and control grids. Acommon cathode is used for both sections. The cathode is biased througha half megohm resistor. A control grid I08 of tube I05 is resistancecoupled to tube 81, reference character I06 indicating the couplingcondenser, and I01 a one hundred thousand ohm resistor for grid I08.

The plates N of tube I are connected to each other and are resistancecoupled to the,

grid II I of one section of a twin triode amplifier II2 of the 1633type. Condenser II3 is a coupling condenser which is connected through aone-tenth megohm resistor II4 to grid III. The grid is grounded througha one-tenth megohm resistor II5.

Tube I I 2 is a cathode follower stage. The purpose of this tube is tocouple the high-impedance output of tube I05 to the low-impedance inputtransformer of the servo amplifier which will be described later on.

Resistance I20 is a twelve hundred ohm bias resistance for cathode I2|of the input section of tube H2. The plate I22 associated therewith isenergized from a source of D. 0. through a fifty thousand ohm loadresistor I23 and is resistance coupled to grid I24 of the output sectionthrough condenser I25, a fifty thousand ohm resistor I26 being the gridresistor. A two thousand ohm resistor I21 is provided in the circuit forcathode I28 which is connected at its ungrounded end through a condenserI29 of large capacity to one terminal of the primary winding I30 oftransformer |3I, the other terminal of the primary being grounded. Withthe arrangement just described, the primary winding of the transformeris shunted across resistance I21 and will be energized in acordance withcurrent variations in the resistance which correspond to those appearingat the tube input circuit.

The voltage applied to grid I03 of tube I05 from rotary transformer 96is 180 out of phase with that of the other control grid I08. Thisvoltage produces an A. C. component in the plate current which varieswith the actual parallax correction.

Thus, the total A. C. plate current component through load resistor I I6is the sum of the above two currents. These component currents are 180out of phase with one another. If they are equal, they balance oneanother in effect, and there is no actual A. C. current through loadresistor H6, and hence no actual A. C. plate current. This is thecondition when the actual and computed corrections are equal. When theactual and computed corrections are not equal, the A. C. grid voltagesof tube I05 are not equal, the two A. C. components of plate current arenot equal, and hence do not cancel. Therefore, under these conditions,there is an A. C. plate voltage which is coupled through condenser II3and tube I I2 to the servo amplifier where it will eventually produce avoltage to operate the elevation correction motor to change the actualcorrection, making it equal to the computed correction.

The elevation servo amplifier comprises two twin triode amplifier tubesI and MI, both of the 1638 type, for the purpose of controlling theoperation of the elevation correction motor 4|, Fig. l, to insert theproper correction in the position of the turret. Motor 4| is of a knowntype and is connected by suitable gearing to the rotors of the elevationdifferential Selsyns as indicated by dash-dot lines.

Cathodes I and I5I of tube I40 are connected to ground through a twohundred ohm resistor I52. Grids I53 and I54 are connected to oppositeterminals of secondary winding of transformer I3I for push pulloperation. Plates I55 and I56 are bridged by condenser I51 and areconnected respectively to grids I58 and I59 of tube I4.I.

Cathodes I60 and I6I are connected through a four hundred ohm resistorI62 to the ungrounded side of the A. C. supply, which is also connectedto grids I58 and I59 through individual twenty-five thousand ohmresistors I63 and I64. Plates I65 and I66 are connected respectively toone terminal of the winding of a relay magnet I61 or I68, whose oppositeterminals are grounded. The windings are bridged respectively bycondensers I69 and I10.

Relay magnets I61 and I68 operate a balanced armature, shown forpurposes of explanation as a double armature |1II12, pivoted at I13 andI14. The armature is spring loaded to assume the neutral position shownwhen the magnetic circuit is balanced. The armatures operate a currentreversing circuit for controlling the operation and direction of motor4I. When either magnet is energized more strongly than the other, thearmature will turn on its pivots and an appropriate pair of contactscarried thereby will make with a pair of stationary contacts. Stationarycontacts I and I16 disposed on opposite sides of the pivot are connectedto a source of direct current and cooperate with armature contacts I11and I18. Similarly, stationary contacts I19 and I80 are grounded andcooperate with armature contacts I8I and I82. The armature members HIand I12 are connected by circuits I90 and I9I to motor 4I. With thearrangement just described, motor 4I will be started in one direction orthe other, depending on which magnet I61 or I68 is more stronglyenergized.

The elevation servo amplifier operates as follows: Both plates I55 andI56 of tube I40 receive a constant A. C.'voltage with respect to theircathodes which are connected to ground through resistor I52. The gridsof this tube receive an A. C. voltage from transformer I3I when theactual parallax correction is incorrect. The size of the A. C. gridvoltage depends upon the size of the error in actual correction. Thephase of the A. C. grid voltage depends upon whether the actualcorrection is too large or too small. Using as a reference the time whenthe A. C. voltage causes the plates to swing positive with respect tothe cathode, one grid, for example, grid I53 will swing positive withrespect to the oathode, while the other grid I54 will swing negativewith respect to the cathode. Therefore, one half of tube I 40 willconduct an appreciable current, while the other half will conduct a muchsmaller current. Thus, for the conditions assumed' the plate current ofplate I55 will be large, and that for plate I56 small.

With no A. C. voltage from transformer I3I, both plate currents areequal. If the plate current for plate I55 has increased and that forplate I56 decreased, plate I56 becomes higher in potential than plateI55, because the voltage drop through resistor I64 has decreased and thedrop through resistor I63 has increased. This happens during each halfcycle when the A. C. voltage on plates I55 and I58 causes both plates toswing positive with respect to the cathode. During each half cycle whenboth plates are negative with respect to the cathode, there is no platecurrent, irrespective of the grid voltages, and both plates tend tobecome equal in potential. The condenser I51 connected between theplates charges quickly during the half cycle when there is plate currentand it discharges slowly when there is no plate current. Hence, anaverage or D. C. plate voltage appears between the plates. For theconditions assumed, plate I56 will be at a higher D. C. potential thanplate I55 with respect to the junction point of resistors I63 and I64.Therefore, grid I59 of tube I4I which is connected directly to plate I56will be at a higher D. C. potential than gri-d I58 which is connected toplate I55, with respect to the cathodes of tube I4I.

Both cathodes of tube I4I' receive an A. C. voltage from the same sourceas the plates of tube I40. When the plates of tube I40 are bothpositive, the cathodes of tube I4 I are also positive, and therefore theplates of tube I4I, which are connected to the ground through thewindings of magnets I61 and I68, are both negative with respect to theircathodes and no plate current flows in tube I4I. During the next halfcycle, the plates of tube I are both positive with respect to thecathodes, and there is a flow of plate current through the windings ofmagnets I61 and I68. The size of each plate current is determined by thegrid-to-cathode voltages in the tube. For the conditions previouslyassumed the grid-tocathode voltage of grid I59 is greater than that ofgrid I58. Therefore, the current flowing through the winding of magnetI68 to plate I66 will be greater than that flowing through the windingof magnet I61 to plate I65.

When equal currents flow through the windings of magnets I61 and I68,equal forces are applied to the balanced armature and a light springloading, not shown, keeps the armature in neutral position which is thecondition when there is no error in the actual correction.

When there is an error, there will be a current in the primary windingof transformer I3I and this will cause an unbalance in the circuits ofrelay magnets I61 and I68. With the conditions already assumed, thecurrent in the winding of magnet I68 will be larger than in the windingof the other magnet and the armature will be attracted, closing contactsI15 and I11 and also I19 and I8I. If, for example, this operation of therelay was due to the actual correction being too large, then theelevation correction motor M will rotate in a direction to decrease theactual correction. When all error is removed, there is no A. C. signalfrom tube I05, the balancer stage, to the servo amplifier, and thearmature I1 I'I 12 will assume its neutral position. If the error in theactual correction were in the opposite direction, then the winding ofmagnet I61 would be the more strongly energized and the opposite set ofrelay contacts I16-I18 and I-I82 would close reversing the polarity ofthe circuit for motor M which would turn in the opposite direction tocorrect the error.

In Fig. 1 a switching means is indicated by reference character I0 forthe purpose of switching the parallax correcting circuit from onecomputer to another. The computer transmitters of the circuits shown inthe drawings are indicated as being associated with a computer A, Whilethe uncompleted bracketed circuits indicated by the legend are connected-to a corresponding circuit arrangement for a computer B, not shown. Theswitching device may be of any suitable kind, for example, a relayarrangement or a rotary switch.

The azimuth parallax correction circuit solves electronically thefunction sin A D 1: cos E for azimuth parallax correction in a similarmanner. A trig-function transformer 200 has its primary windingsconnected to the coarse azimuth differential stator circuits 20I, 202,and 203. The

secondary winding 204 of the transformer is bridged by two seriallyconnected forty thousand ohm resistors 205 and 206 whose junction pointis connected by circuit 201 and condenser 208 to the control grid 209 ofa super control tube 2I0 of the 6SK'1 type. The output of transformer200 is an A. C. voltage proportional to sin Ag.

The primary winding of trig-function transformer 2 is connected tocircuits 46, 41 and 48 of the stator of coarse elevation differentialSelsyn 34. The output of this transformer is an A. Cuvoltageproportional to cos Eg. This voltage is too small to be applied directlyto tube 2I0 so therefore it must be amplified. To this end, one terminalof the secondary winding 2I2 of the tarnsformer is grounded and theother terminal is connected via circuit 2 I 3 to the grid of a triodevoltage amplifier 2 I4 which is of the 6J5 type. The output of tube 2I4is a voltage proportional to cos Eg, the A. C. component of which is fedthrough a condenser 2 I5 to a cathode of a double diode 2I6 of the 6H6type. The corresponding plate 2II of the diode is connected to groundthrough a one half megohm resistor, and through another half megohmresistor 2I9 to the control grid 209 of tube 2I0. The output from tube2I6 is a negative D. C. voltage proportional to cos Eg- The negattive D.C. voltage from tube 2 I 6 varies the amplification factor of tube 2 Iinversely with cos Eg. The A. C. voltage sin Ag is the grid signalvoltage. The A. C. plate voltage of tube 2 I0 varies as the product ofthe grid voltage and amplification factor and is equal therefore to sinA /cos Eg- Plate 220 of tube 2I0 is connected through a load resistor22I to a source of D. C. potential and through condenser 222 to thecontrol grid 223 of a tube 224 which is similar to tube 2). Control grid223 is also connected through a half megohm resistor 225 to a plate ofrange double diode 90. The plate of tube 224 is resistance coupledthrough condenser 226 to a control grid 221 of double pentode 228, of atype similar to tube I05. From this point on, the elevation and azimuthparallax correction circuits and the apparatus controlled thereby areidentical, so the remainder of the elevation correction circuits will bebriefly described.

The amplification factor of tube 224 is varied by the negative D. C.voltage from the plate of the range diode 90. It will be recalled thatthis voltage is directly proportional to range. Since the A. C. voltageon the grid of tube H0 is proportional to sin Ag/COS Eg, the effect ofthese grid voltages is to give an A. C. plate voltage componentproportional to sin Ag/COS EgXDO. This is the voltage proportional tothe computed azimuth parallax correction.

A rotary transformer 230, similar to transformer 96 has its rotorwinding 23I connected by leads 232 and 233 to opposite terminal-s ofpotentiometer 234, the adjustable arm 235 of which is connected to asecond control grid of tube 228. As in the similar circuits of tube I ofthe elevation correction circuit, the computed correction voltage iscompared with the actual correction voltage from transformer 230 and thenet output of tube 228 is an A. C. voltage, the magnitude of whichdepends upon that of the error in correction, and the phase of whichdepends upon whether the correction was too large or too small. Thisvoltage is coupled through a cathode follower stage comprising a doubletriode 240 to the primary winding of transformer 24I which is the inputfor the azimuth servo amplifier. In this amplifier, twin triodes 242 and243, current reversing relay 244, and azimuth correction motor 40 whichis controlled by the relay over leads 245 and 243, all function toeffect azimuth parallax correction in the same manner as elevationparallax correction is accomplished by corresponding elements of theelevation circuits.

The circuits just described compute parallax correction where thecontrol station and gun turrets are disposed along a common longitudinalaxis of the ship. If the gun turrets were placed in the wings of theairplane or otherwise offset from the zero azimuth axis, the correctioncir- 12 cuits must be such as to take into consideration the distance(S) that the turret is spaced from the computer and the azimuth angle(a) at which the turret is displaced from the control station.

Depending on the position of the target with respect to the computer andturret, the gun aiming angles of the computer in azimuth and elevationwill differ from those of the turret due to parallax and this differencemust be corrected so that the turret guns are aimed at the properangles.

The azimuth parallax correction angle (EA) is equal to the diiferencebetween the azimuth angle of the target relative to the gun turret andthe azimuth angle of the target relative to the computer (Ag) Likewisethe elevation parallax correction angle (2E) is equal to the differencebetween the elevation angle of the target relative to the gun turret andthe elevation angle of the target relative to the computer (Eg) It hasbeen determined empirically that the azimuth and elevation parallaxcorrections may be approximated as S sin (er-A ZA D cos E9 and Thesefunctions are computed electronically in a second embodiment of theinvention illustrated by the block diagram of Fig. 3. A block diagram isthought best under the circumstances as the actual circuits of thesecond embodiment require a substantial duplication of those of Figs. 1and 2 with similar functions plus two other like circuits for furtherfunctions. From what has gone before, it is thought that no diflicultywill be experienced in understanding the present embodiment as describedin connection with a block diagram.

The present embodiment contemplates selfsynchronous control circuitslike those of Fig. 1 having correction introduced therein by servoamplifiers as described. Four similar trig-function transformers areused as well as a voltage proportional to range for controlling theinputs to the parallax correction circuits.

In the diagram of Fig. 3, two squares 300 and 30I represent electronicreciprocal circuits, both having an input connected to the voltagesource sin A cos A D D The output of the reciprocal circuit of block 300is connected to an input of an electronic multiplier circuit 302 and toan input of an electronic and - reciprocal circuit 303. The output ofthe sin Eg trig-transformer is connected to an input of multipliercircuit 302 and also to the input of another multiplier circuit 304. Theoutput of multiplier 302 is the product of its two inputs or sin E g sinA D0 The output of the reciprocal circuit of block 30I is connected toan input of a multiplier circuit 304 and also to an input of reciprocalcircuit 305. The output of the multiplier circuit is the product of bothitsinputs or sin E, cos A, o

The actual circuit and its method of operation for determining thelatter function is similar to that described in connection with thefirst embodiment of the invention.

The output of the cos Eg trig-transformer is connected to a second inputof each reciprocal circuit 305 and 303. The output of the former is cosA D cos E g and the latter which is the-same as that for azimuthparallax correction described in the earlier embodiment and obtained inthe same manner.

The outputs of multipliers 302 and 304 are connected to the primarywindings of functional transformers 306 and 301 whose turn ratios areproportional to S. sin a, and S. cos a, respectively, the output of thetransformers being an A. C. voltage proportional to input voltage andthe transformer function.

The transformers 306 and 301 may have single secondary windings where agun turret is controllable from a single control station. Where a turretis controllable from any of a plurality of spaced control stations, thefunctional transformers may be modified by providing a correspondingnumber of secondary windings each having an appropriate turn ratioproportional to S. sin a and S. cos a of the turret with respect to thedifferent control stations in order that when the turret is switchedfrom one station to another the circuits will be compensated for changedspacing and relative angular position of the turret and control station.

In the present case it is assumed that two spaced control stations A andB are employed, either of which may be selectively connected to theparallax correction circuit by the operation of switch l of Fig. 1.

The parallax corrections 2A and 2E are the same as referred to aboveexcept that the functions for respective control stations are identifiedby sub A or sub B and will have different values owing to the spacing ofthe control stations.

For the two control station arrangement transformers 306 and 307 areshown with two sets of serially connected secondary windings either setbeing selectively connected in circuit by switch I0.

Secondary winding 3l5 has one terminal grounded and the other connectedthrough secondary winding 3|! of transformer 301 to contact 323 ofswitch l0 which is closed when the parallax correction circuit isconnected to computer B, contact 323 being connected to the azimuthservo amplifier by the switch. 7

As already stated, the turn ratio of transformers 306 and 301 is suchthat their output is a voltage proportional to the product of theirinputs and S. sin a and 8'. cos a respectively.

Since the input of transformer 306 is sin A, sin E o then the output is,with the described secondary winding connection,

sin E g D0 The input for transformer 30'! is sin A sin 04 cos A, sin E,0

which when multiplied by the transformer, becomes at the output sin E ocos A cos a sin E S D0 which is the elevation parallax correction forcomputer B. This voltage is connected via contact 323 of switch [0 tothe elevation servo amplifier input circuit, where it is utilized in thesame manner as the voltage from the plate of tube 81 of Fig. 2 formaking the required parallax correction.

When the A computer is in use, secondary windings 3l6 and 3! oftransformers 306 and 301 are connected in circuit with the elevationservo amplifier by switch l0, windings M5 and 3 being disconnected atthis time by the switch. Since the A computer is assumed to have aspacing from the turret differing from that of computer B, the turnratios of the transformers with secondary windings 3H3 and 3; in use isproportional to SA sin Q11 and SA cos M respectively.

The combined output voltages of the transformers is a voltageproportional to cos (a A or {IE3 sin E which is the elevation parallaxcorrection for computer A. This voltage is connected via contact 3 I4 ofswitch l0 to the elevation servo amplifier for use in the same manner asthe voltages from secondary windings M5 and 3H.

The circuits associated with transformers 308 and 309 are generally thesame as those of transformers 306 and 301.

Transformer 308 has two secondary windings 3H) and 320 and transformer309 also has two secondary windings 32| and 322. Secondary windings 3| 9and SH are connected in series, one terminal of winding 3|9 is connectedto contact 325 of switch I 0 and a terminal of winding 32! is connectedto ground. The secondary windings just mentioned are used in connectionwith the B computer, and the turn ratios are such that the inputvoltages are multiplied by SB sin (15 and SB cos as respectively. Theprimary windings of the transformers are respectively connected to theoutputs of reciprocal circuits 305 and 303 whose output voltages areproportional to SA cos -A or ZE cos A D cos E g sin A,, D cos E g andsince the functional transformers multiply their input viltages inaccordance with their turn ratios, the output of transformer 309, withthe connections described, is a voltage proportional to S sin A, cos D0cos E,

and that of transformer 308 is a voltage proportional to S cos A, sin Docos E,

These, voltages are added together in proper phase and their sum is SBSin B s) D0 cos E which is the azimuth parallax correction ZAB forcomputer B. This voltage is connected via contact 325 of switch It tothe azimuth servo amplifier where it is used in circuit arrangement tocontrol the amplifier in the same manner as the voltage from the plateof tube 224, Fig. 2, to effect azimuth parallax correction.

Secondary windings 320 and 322 operate in the manner just described whenthe A amplifier is in use. With the latter windings in circuit, the turnratios of transformers 388 and 309 are S. sin cm, and SA cos an,respectively, and the sum of their output voltages is SA SlIl (IA-A51 D0cos E,

which is the azimuth parallax correction 2AA for computer A. Thisvoltage is connected to the servo amplifier control circuit via contact328 of switch I0 when the A computer is in use.

As many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrativ and not in a limiting sense.

What is claimed is:

1. In an aiming system wherein a control device transmits aiming angledata over selfsynchronous transmission means to a gun positioningdevice, the improvement which comprises, in combination, means forderiving from signals transmitted over said transmission means aplurality of different voltages, said voltages being proportional tosines and cosines respectively of azimuth and elevation angle datatransmitted over said transmission means, means providing a voltageproportional to range, a device controlled by the range voltage andthose proportional to the sines and cosines for deriving voltagesproportional to parallax correction angles, transformer meansinterconnected with the selfsynchronous transmission means, and meansfor controlling said transformer means by the derived voltages tocorrect the aiming angle data for parallax.

2. In an aiming system wherein a control device transmits aiming angledata over selfsynchronous transmission circuit means to a gunpositioning device, the improvement which comprises a plurality oftransformers energized by signals transmitted over the transmissionmeans having turn ratios adapted to produce output voltages respectivelyproportional to sines and cosines of transmitted elevation and azimuthaiming angles, means providing a voltage proportional to range, meansjointly controlled by 16 the latter voltage and the output voltages ofthe several transformers for deriving voltages proportional to parallaxcorrection angles for the gun positioning device, rotary differentialtransformer means in the transmission circuit means adapted with changesin the angular position of the rotary member means thereof to effect acorresponding change in the transmitted aiming angle data, rotaryinductive means coupled with the rotary member means of the differentialtransformer means having linear output voltages, the magnitude of whichis controlled by the angular position of the rotary differentialtransformer means, means for comparing the last mentioned outputvoltages with those proportional to parallax correction, and meanscontrolled by a difference in said voltages for effecting angularmovement of the differential transformer means as Well as the rotaryinductive means until a difference no longer exists, whereby thedifferential transformer means are positioned so that the aiming angledata received at the gun positioning device is corrected for parallax.

3. In an aiming system wherein a control device transmits aiming angledata over selfsynchronous transmission circuit means to a gunpositioning device, the improvement which comprises a plurality oftransformers energized by signals transmitted over the transmissionmeans having turn ratios adapted to produce output voltages respectivelyproportional to sines and cosines of transmitted elevation and azimuthaiming angles, means providing a voltage proportional to range, meansjointly controlled by the latter voltage and the output voltages of theseveral transformers for deriving voltages proportional to parallaxcorrection angles for the gun positioning device, rotary differentialtransformer means in the transmission circuit means adapted with changesin the angular position of the rotary member means thereof to effect acorresponding change in the transmitted aiming angle data, rotaryinductive means coupled with the rotary member means of the differentialtransformer means having linear output voltages, the magnitude of whichis controlled by the angular position of the rotary differentialtransformer means, means for further adjusting said voltages tocompensate for the spacing between said devices, means for comparing theadjusted last mentioned output voltages with those proportional toparallax correction, and means controlled by a difference in saidvoltages for effecting angular movement of the differential transformermeans as well as the rotary inductive means until a difference no longerexists, whereby the differential transformer means are positioned sothat the aiming angle data received at the gun positioning device iscorrected for parallax.

4. In an aiming system wherein a control device transmits aiming angledata over self-synchronous transmission circuit means to a gunpositioning device, the improvement which comprises a plurality oftransformers energized by signals transmitted over the transmissionmeans having turn ratios adapted to produce output voltages respectivelyproportional to sines and cosines of transmitted elevation and azimuthaiming angles, means providing a voltage proportional to range, meansjointly controlled by the latter voltage and the output voltages of theseveral transformers for deriving voltages proportional to parallaxcorrection angles for the SRCH RGUM gun positioning device, rotarydifferential transformer means in the transmission circuit means adaptedwith changes in the angular position of the rotary member means thereofto eifect a corresponding change in the transmitted aiming angle data,rotary inductive means coupled with the rotary member means of thedifferential transformer means having linear output voltages, themagnitude of which is controlled by the angular position of the rotarydifferential transformer means, means comprising a potentiometer forfurther adjusting said voltages to compensate for the spacing betweensaid devices, means for comparing the adjusted last mentioned outputvoltages with those proportional to parallax correction, and meanscontrolled by a difference in said voltages for effecting angularmovement of the difierential transformer means as well as the rotaryinductive means until a difference no longer exists, whereby thedifferential transformer means are positioned so that the aiming angledata received at the gun positioning device is corrected for parallax.

5. In an aiming system wherein a control device transmits aiming angledata over transmission means to a gun positioning device, a parallaxcorrection circuit comprising means controlled by signals transmittedover the transmission means for producing a voltage proportional to theproduct of the sine of the elevation angle and cosine of the azimuthangle of the transmitted data, a vacuum tube having its grid energizedby said voltage, and a source of negative potential increasing withrange for biasing said grid whereby the output voltage of the tubevaries as the product of the sine of the elevation angle and cosine ofthe azimuth angle divided by range.

6. In an aiming system wherein a control device transmits gun azimuth,Ag and elevation, Eg, aiming angle data over transmission means to a gunpositioning device, a parallax correction circuit comprising meanscontrolled by signals transmitted over the transmission means forproducing a voltage proportional to sin A,

cos E,

of the transmitted angle data, a vacuum tube having a rid circuitenergized by said voltage, a source of negative potential increasingwith range (Do) means for biasing said grid from said source whereby theoutput of the tube is proportionalto SsinE,

'sin A sin a D and S sin E, o

where S is the distance between the device and a. is the azimuth angleof the gun positioning device with respect to the control device, meansfor adding the product voltages whereby the sum of the voltages S sin E,cos (a-A,) 0

obtained is proportional to the elevation parallax correction voltage,and means comprising adjustable differential transmformer meansinterconnected with the transmission means and controlled by the lastmentioned voltage for effecting elevation parallax correction in saidangular data.

8. In an aiming system wherein a control device transmits gun azimuth,Ag and gun elevation, Eg, aiming angle data over transmission means to agun positioning device offset therefrom by the distance S and b azimuthangle a, means providing a voltage proportional to range, Do, a parallaxcorrecting system controlled by signals transmitted over said voltageand by said transinitting means for deriving voltages proportional -cosA, cos a sin E, o and sin E, cos A, o

a pair of transformers having turn ratios respectively proportional toS.sin a and 5.00s 0:. having their primary windings energized by therespective voltages and their secondary windings connected in series,the combined output voltages of the secondary windings being a voltageproportional to 8. sin E, cos (a-A,) 0

and means comprising adjustable differential transformer meansinterconnected with the transmission means and controlled by the lastmentioned voltage for effecting elevation parallax correction of theaiming angle data.

9. In an aiming system wherein a control device transmits gun azimuth,Ag, and gun elevation, Eg, aiming angle data over transmission means toa gun positioning device offset therefrom by the distance S and byazimuth angle a, means providing a voltage proportional to range. Do. aparallax correcting system controlled by signals transmitted over saidvoltage and by said transmitting means for deriving voltagesproportional to cos A, D cos E,

and

sin A, D cos E,

-cos A sin a D cos E,

and

---sin A 0 ea D cos E, 0

19 means adding said resultant voltages whereby a voltage S Sill (a-A Dcos E,

is obtained which is proportional to azimuth parallax correction. andmeans comprising adjustable differential transformer meansinterconnected with the transmission means and controlled by the lastmentioned voltage for effecting a corresponding correction of the aimingangle data.

10. In an aiming system wherein a control device transmits gun azimuth,Ag, and'gun'elevation, s, aiming angle data over transmission means to agun positioning device offsettherefrom by the distance S and byazimuth'angle a, means providing a voltage proportional to'range, Do, aparallax correctingsystem'controlled by signals transmitted over saidvoltage and by said 20 transmitting means for deriving voltagesproportionalto cos A a D cos E,

and

sin A 8 D cos E g a pair of transformers having turn ratios respectivelyproportional to S.sin a and S cos a energized by the respective derivedvoltages, the secondary windings of the transformers being connected inseries, their combined output voltages being a voltage proportional toS.sin E cos (or-A o 20 and means comprising adjustable differentialtransformer means interconnected with the transmission meansandicontrolled by the last mentioned voltage for effecting azimuthparallax correction of the aiming angle data.

GIFFORD E. WHITE. ROBERT L. GRAEF. CHARLES J. LA FORGE.

REFERENCES CITED The following references are of record in the file ofthis patent: V

UNITED STATES PATENTS Number Name Date 821,521 Moody May 22, 19061,173,094 Blume Feb. 22, 1916 1,200,233 Preston Oct. 30, 1916 1,242,649Brand Oct. 9, 1917 ,612,117 Hewlett et a1. Dec. 23, 1926 1,637,039Hewlett et a1 July 26, 1927 1,755,975 Willard Z. Apr. 22, 1930 2,129,880Scherbatskoy Sept. 13, 1938 2,151,718 Riggs Mar. 28, 1939 2,244,369Martin June 3, 19 1 2,359,768 Kiltie Oct. 10, 1944 2,405,028 Ford July30, 1946 2,408,081 Lovell et a1 Sept. 24, 1946 2,421,230 Agins May 27,1947 0,798 McCarthy Feb. 8, 1949 OTHER REFERENCES Ser. No. 212,349,Papello (A. P. (3.), published May 25, 1943.

